function [ DrI ] = getDrI( r, rn, I )
%GETDRI Summary of this function goes here
%   Detailed explanation goes here

s = 1 / rn;
A = I;
ds = -r / rn^3;
dA2 = zeros(27, 1);
dA = reshape(dA2, 3, 3, 3);

DrI = tensorProductGradient(s, ds, A, dA);

end

